When building a home wheelchair ramp, nothing is more critical than slope. Anything more than a 1-to-12 ratio is unacceptable. Why? Because slopes steeper than this may be beyond the strength of people using manual wheelchairs trying to use the ramp. It may also cause an electric wheelchair to tip backwards.

What is slope? Simply put, slope is the relationship of vertical height (rise) to horizontal length (run). A gentler slope, say a 1-to-16 ratio, will require a longer wheelchair ramp than a 1-to-12 ratio.

Using slope, how do I determine how long my ramp will be?

First, measure the distance between the bottom of the entry point (front door, for example) to the grade at the house’s foundation. For our purposes, suppose that distance is 30 inches. Then measure the change in grade between the foundation and where the wheelchair ramp’s bottom landing will be located. If it’s 10 inches lower, then that figure will factored in.

Second, after you’ve made those measurements, do some basic math. Say that a ramp with a 1:12 slope is to be built with a home with a 40-inch total rise.

Multiply 40-inches by 12. That number is 480 inches. Convert it to feet, and the length of your ramp (excluding all landings) will be 48 feet to safely accommodate wheelchair access at a 1:12 slope.